Virtual keyboards are increasingly used all over the world in various devices such as tablet computers and/or smart-phones (e.g. iPhones™, iPads™) typically including a touch screen enabling to use standard virtual alphanumeric keyboards. These alphanumeric keyboards typically include letter keys, punctuation mark keys, number keys and optionally function keys. These various keys and especially the letter keys add up to quite a large number of keys and when used in reduced compact devices such as mobile phones designed to be held by a single hand and placed in a person's pocket, can become extremely uncomfortable to use. For example, in the English language there are twenty-six letters requiring twenty-six different letter keys each representing a different letter. In this case, even when only using letter keys in a virtual keyboard, if the touch screen is too small, which is usually the case in reduced input devices such as smart-phones, in which touch screen is typically smaller than that of a tablet computer, it can be quite cumbersome and uncomfortable to press each letter key since the screen size reduction results in key size limitations. Therefore, reducing the number of keys required for inputting letter characters through the virtual keyboard can dramatically improve utilization of reduced or any other type of touch screens.
U.S. Pat. No. 5,307,267 by Yang Gong M. teaches a keyboard input device that includes symbol keys where a combination of symbol keys can be interpreted as a character if all respective symbol keys are simultaneously pressed by a user
A patent application No. WO2007039746 by Maber Jonathan discloses a keyboard for entry of text characters that comprises: a plurality of keys and a processing means for detecting when at least one of the plurality of keys is pressed. Each of the plurality of keys has an indicia marked on its surface. When the processor detects that two or more of the plurality of keys have been pressed within a predetermined time period of each other, data corresponding to a text character visually resembling the combination of the indicia marked on the two or more of the plurality of keys is output. A corresponding method of text entry is also described. The output from the keyboard visually resembles the combination of the indicia on the keys.
U.S. patent application No. 2005104750 by Tuason Christopher discloses a compact keypad enabling direct single-press-per-character data entry, which is made possible by the use of adjacent combination key-press entries. The keys are sufficiently sized and spaced to enable the direct activation of any of a set of characters comprised of numbers, letters and symbols with a single finger stroke of either one individual key, or an adjacent combination of keys. According to Tuason the keys of the keypad, regardless of their individual shape or layout as a group, are placed in close enough proximity to allow two adjacent keys to be depressed either one-at-a-time, or both simultaneously by a single, one finger key stroke to code for a desired alphanumeric character, symbol, or arithmetic function.
Although these methods allow reducing the number of letter keys required, depending on symbols selection, when using a small compacted input device such as a mobile phone, making it possible to slightly enlarge the size of each key, it may be complicated and cumbersome for a user to remember the symbols combination that are required to build each character and to press them simultaneously. Moreover, simultaneously pressing of keys may often require using more than one hand and/or more than one finger to carry out this task, which may be a difficult or annoying for users who wish to use one hand/finger for pressing keys (e.g. for writing text message using their smart-phone) or even impossible for people having handicaps that only allow them to use a single finger, hand and the like.